1. Field of the Invention
The present invention relates to a display device and its driving method.
2. Description of the Prior Art
Recently, liquid crystal display devices have been noticed as flat panel devices of light weight and low power consumption. In particular, an active matrix liquid crystal display device provided with a thin film transistor (referred to as TFT, hereinafter) at each display pixel has been widely used as various displays such as TV and OA (office automation), because high definition display pictures can be obtained without any cross-talk. In addition, recently, there exists such a trial that the liquid crystal display device is used as a projector type display device according to a demand of still larger-sized display pictures.
When the active matrix display device as described above is used as a projector of smaller size, lower cost, and lower power consumption, it is essential to reduce the size of its optical system. Further, it is also necessary to reduce the size of the liquid crystal display device itself as small as about 3 inches, for instance.
Therefore, in the above-mentioned display device, there exists a trial of forming both a display pixel section and a driving circuit section for driving respective display pixels on the same substrate integral with each other.
On the other hand, it has become important to allow the display device to correspond to a plurality of image or video standards, for instance such that a picture having an aspect ratio of 4:3 based upon computer image signals is displayed on a display device composed of pixels having an aspect ratio of 16:9. In this case, it is considered that the number of the horizontal pixels including the horizontal blanking period of video signals is smaller than the number of the display pixels for constructing one horizontal pixel line on a display panel. In the case as described above, non-display data are displayed at the display pixels where corresponding video signals do not exist. In this case, as the method adopted on the driving circuit side, although it may be considered to bury the non-display data previously during the horizontal scanning period of the video signals, by changing the driving frequency of the video signals by use of a frame memory, the cost of this method is relatively high.
As another method, it may be considered to prepare both the display data and the non-display data and to select the display data or the non-display data for each pixel on the display device side in conformity with the video standard. The method of driving the display device as described above is disclosed SID 93 DIGEST p.383 to p.386 "A 1.9-in, 1.5-M pixel Driver Fully-Integrated Poly-Si TFT LCD for HDTV Projection", for instance, in which a driving circuit mainly composed of shift registers for transferring video signals in sequence is used. In this method, however, it is difficult to switch the signal lines driven in the display panel in conformity with the video signal standard.